The present invention is directed to a fluid flow sensor, and more particularly, to a thermal based thin film sensor for determining the velocity of fluid flow.
Thermal based thin film systems are typically used as flow sensors to determine the velocity of gas flowing over the sensor. When fluid flows over the sensor, the flow distorts a set of generated isotherms (i.e., the heat field) which can be at least partially detected by a heat sensor. Typically, a plurality of such fluid flow sensors are located on a surface, such as an air foil, where local velocity, temperature, angle of attack and angle of sideslip of the fluid flow are of critical interest. Furthermore, ground or flight based weather anemometry requires both a direction and a magnitude of air flow. In order to measure both the direction and velocity of the fluid flow, a plurality of fluid flow sensors are typically spaced across the surface of interest.
When the fluid flow reaches higher velocities, the temperature of the heat source must be increased to accurately measure velocity. However, the temperature of the heat source can be increased to only a certain level before the heat source and/or sensor is damaged. When the fluid reaches a speed above that which can be sensed by the thin film sensor, a system of pressure sensors spaced across the surface are typically utilized to determine velocity of the flow. Each pressure sensor is pneumatically connected to the surface by a pressure tap.
In such a system described above, a plurality of sensors and a plurality of pressure sensors must be located across the surface. Each individual pressure and heat sensor must be mounted to the surface and connected to a processor. Each additional sensor also requires additional power. Furthermore, the resultant array of sensors may also create a relatively highly observable feature on the surface with respect to radar and infrared signatures.
Accordingly, there is a need for a small, compact, and efficient flow sensor that can accurately measure a wide range of flow velocities and directions.
In one embodiment, the present invention is a flow sensor which includes a central heat source and a pair of non-linearly aligned heat sensors such that the sensor, acting alone, can accurately determine the direction and magnitude of the fluid flow. The sensor may include an integral pressure sensor, thereby eliminating the need for separate pressure taps and pressure sensors on the surface and increasing the dynamic range of the sensor (i.e. the range of velocities that can be measured by the sensor). The sensor may also include a substrate temperature sensor for sensing the temperature of the substrate of the sensor. The sensor may also include an isolated fluid temperature sensor to measure the temperature of the surrounding fluid.
In one embodiment, the invention is a flow sensor for determining the velocity and direction of a fluid flow including a die, a heat source located on the die, and a first and a second heat sensor located on the die to detect at least a portion of heat generated by the heat source. The first and second heat sensors and the heat source are arranged in a non-linear orientation.
Other objects and advantages of the present invention will be apparent from the following description and the accompanying drawings.